ALMA MATER STUDIORUM

UNIVERSITA' DI BOLOGNA

SCUOLA DI SCIENZE

Corso di Laurea Magistrale in

BIOLOGIA MARINA

A first survey on the status of the Posidonia oceanica meadow

in Calpe Bay (Alicante, Spain)

Tesi di laurea in

Alterazione e conservazione degli habitat marini

Relatore: Presentata da:

Prof. MARCO ABBIATI MARTINA SCANU

Correlatore

Dott. JOSE RAFAEL GARCIA-MARCH

Anno Accademico 2016/2017

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SUMMARY

1. Introduction……………………………………………………………...…...3

1.1 Evolutionary history……………………………………………………………..…3

1.2 Habitat distribution……………………………………………………………...….4

1.3 The plant…………………………………………………………………..…..……5

1.4 Ecology……………………………………………………………………………..8

1.5 Structure of meadows………………………………………………………………9

1.6 The role of Posidonia oceanica meadows in coastal systems………………………9

1.6.1 Ecological role……………………………………………………………9

1.6.2 Physical role…………………………………………………………..…12

1.6.3 Economical role…………………………………………………………12

1.6.4 Bioindicator role………………………………………………………...13

1.7 The causes of regression………………………………………………………..…16

1.8 Policies apllying to Posidonia oceanica meadows………………………………..18

2. Work prupose……………………..……………………………………...…21

3. Materials and methods……………………………………….…………….22

3.1 Study area…………………………………………………………………………22

3.1.2 Geological context……………………………………………………....23

3.1.3 Marine context……………………………………………………….….24

3.2 Physical descriptors……………………………………………………………….25

3.2.1 Water conditions………………………………………………………...25

3.2.2 Sediment analysis………………………………………….……………26

3.3 Monitoring Posidonia oceanica…………………………………………………..29

3.3.1 Statistical analysis…………………………………………………….…33

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4. Results…………………………………………………………………...…..34

4.1 Physical descriptors……………………………...…………………………….….34

4.1.1 Water conditions………………………………………………………...34

4.1.2 Sediment analysis…………….………………………………………….38

4.2 P. oceanica monitoring results…………………………………………………….44

5. Discussion……………………………………………………...……………53

6. Conclusion…………………………………………………..………………60

7. References…………………………………………………………………...59

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1. Introduction

Posidonia oceanica (Linnaeus) Delile, (1813) is a marine plant,

with roots, vascular trunks, leaves and flowers. The name

“Posidonia” was put in honor of Poseidon, god of the sea, while the

Latin name “oceanica” was given by Linnaeus, however is

misleading since this species is not found in the Atlantic ocean

(Cabioch et al., 1995).

1.1 Evolutionary history

About 120-110 million years (Ma) ago, in the Cretaceous period, some continental

angiosperms, the Phanerogams, returned to the marine environment. Further back in time, about

475 Ma ago, in the Ordovician (Primary era), their distant ancestors had left the marine

environment to colonize the continents (Wellman et al., 2003).

By the number of their species in today’s natural environment, marine angiosperms represent

rather a small group: 13 genera and 60 species (Kuo et al., 2011). For purposes of comparison,

there are 234 000 angiosperms species (almost all continental) and about ⁓2.2 million (60.18

million SE) marine species of fauna and flora together (Fredj et al., 1992, Heip et al., 1998,

Mora et al., 2011). There are three hypothesis that could explain this big difference in the marine

and terrestrial number: (1) the predominance of vegetative reproduction compared to the sexual

one for marine angiosperms, excludes genetic recombination and turn off the evolutionary

motor (Romero 2004). (2) The absence of mutualistic symbiosis with insects for pollination

reduces the speciation events (Romero 2004). (3) Lastly, the competitive advantage the marine

angiosperms have over other marine primary producers is so great that competition has not

driven evolution (Boudouresque 2012).

However, although the marine angiosperms are not numerous, their ecological role is

considerable in coastal environments: many of them are ecosystem engineers or at least key

species. The ecosystems they build up or in which they are the major actors, play an essential

role in many parts of the world. This is true for the Mediterranean sea (Boudouresque 2012),

where in addition to P. oceanica there are other species of seagrasses whose (Table 1.2).

Taxonomic classification

Empire

Kingdom

Phylum

Subphylum

Infraphylum

Superclass

Class

Order

Family

Genus

Species

Eukaryota

Plantae

Tracheophyta

Euphyllophytina

Spermatophytae

Angiospermae

Monocots

Alismatales

Posidoniaceae

Posidonia

oceanica

Table 1.1 Taxonomic

classification of P. oceanica

(AlgaeBase).

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Species Distribution Habitat

Maximum

depth (m)

Rhizome

diameter

(mm)

Leaf

length

(cm)

Leaf

width

(cm)

Hypogea

biomass

(gdw m-2)

Posidonia

oceanica

Mediterranean

Sea, stops at the

border line where

Mediterranean

and Atlantic

waters mix

Common on

sandy

bottoms, is

often found on

rock and

coralline

50 10 115 1.2 6526

Cymodocea

nodosa

Widely

distributed

throughout the

Mediterranean,

around the

Canary Islands

and down the

North African

coast

Common on

sandy

bottoms, it

prefers calm

hydrodynamic

environments

40 2 40 0.36 324

Zostera

marina

Limited and

pointform;

reported in Italy

Common on

sandy and

muddy

bottoms, it

suits low-salt

waters, low

tolerance to

desiccation

7 3.5 60 0.6 Min 21

Max 161

Zostera noltii

Widely

distributed

throughout the

Mediterranean

Common on

sandy and

muddy

bottoms, it

suits low-salt

waters

6 1.3 40 0.10 Min 31

Max 62

Halophila

stipulacea

Present in the

eastern

Mediterranean,

reported in Italy

Common on

sandy bottoms 30 1.3 7 0.7 -

Table 1.2 Summary of the main characteristics of the Mediterranean seagrasses (modified from Buia et al., 2003)

1.2 Habitat distribution

Currently, the genus Posidonia presents a bipolar distribution:

of the 9 known species, P. oceanica is endemic to the

Mediterranean Sea, while the other 8 species are widespread in

the seas of Australia. P. oceanica is present almost throughout

the Mediterranean sea. Its range of distribution finishes just

before the Strait of Gibraltar on the west side (Conde Poyales

1989), and it is absent from the Egyptian coast to Lebanon (Por

1978) on the east side (Fig. 1.1). Figure 1.1. Geographical distribution of P.

oceanica in European coastal waters. (Borum

et al., 2004).

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It is known that most of the Mediterranean sea dried up in the Messinian period, 5.6 to 5.3

million years ago, because of the closing of the Strait of Gibraltar, but is unknown how P.

oceanica survived this crisis. Maybe refuge areas existed, from which it could recolonize the

Mediterranean after the Gibraltar Strait reopened (Boudouresque et al., 2012).

P. oceanica is the only seagrass colonizing in a continuous way the coastal zone between the

surface and the 40 m depth (Buia et al., 2003), is unique among seagrasses in that it can thrive

on either rock or sand (Giovannetti et al., 2008).

1.3 The plant

P. oceanica is made of horizontal and vertical

stems, more or less woody, usually buried in the

sediment, called rhizomes. They can be of two

types: the horizontal called plagiotropic, and the

erect orthotropic (Fig. 1.2); there is not a

functional differentiation between these

rhizomes, and the environmental conditions can

determine the growth pattern. The vertical

growth is favored in areas were sediment

deposition is very intense, whereas the horizontal

one promote the extension of the seagrass beds

and plant tends to colonize or re-colonize the

substratum.

Regardless of the type, the rhizomes support

shoots (Fig 1.3) made by a little group of leaves,

generally 4-8. Leaves are 8-11 mm wide and may

reach 150 cm in length. In the shoot, they present

an alternate disposition, being the central leaves

the youngest and the external the oldest. Leaf

growth zone (meristem) lies at its base. Every leaf

consists of a base (petiole) and of the limbo. The

limbo is the visible part of the leaf, is from green

color to dun, according to the leaf age, and it can be densely covered by organisms that are

Figure 1.2. Anatomical details.

Figure 1.3. Shoots and leaves details (Buia et al. 2003).

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fixed on, the epiphytes. The petiole is almost not pigmented, it is fibrous and the real leaf

appears after it. It can measure up to 5 cm and is separated from the limbo by a semicircular

mark (lanula), which is where the split takes place in the fall of the leaf. The morphological

features allow to classify leaves in: juveniles less than 5 cm long, intermediate longer than 5

cm and adult when a petiole is formed (Giraud et al., 1979, Boudouresque et al 1983).

When they die, the leaves do not fall off at all, the

basal leaf (petiole), remains attached to the

rhizome (Fig. 1.4). The vegetative season is all

year, leaves are formed and drop all year round

(Pergent et al., 1991). Detached leaves are not

very putrescible, and they can last for several

centuries, creating a peculiar habitat for

detritivorous invertebrates. The analysis of the

age and growth of the plant based on leaf

structure is known as lepidochronology (Crouzet

et al., 1983). This is a powerful tool for measuring the speed of growth, past primary production,

old pollutant levels, etc. (Pergent et al., 1990).

Generally leaves live between 5 and 8 months and more rarely up to 13 months. This species

presents a peculiar life cycle, with a few marked seasonal

variations, being in the leaves better where it is estimated. It

is possible to speak about several phases. The juvenile phase,

or of hard latency, from October to February. During this

period new, short leaves are formed with few epiphytes. The

phase of maturity or activity is from March to June, and

though new leaves are not generated, the existing ones

present a very rapid growth. The phase of old age or of

sluggish growth lasts from June to September, and during

this period the growth is diminishing to the minimum; in the

center of the bundle, a great number of leaves appear. At the

same time, the existing leaves are aging and reach their

maximum heights, and are loaded with epiphytes, reducing

its photosynthetic efficiency. Though the loss of the leaves

Figure 1.4. Characteristic rhizomes, consisting largely of

petiole, basal part of the leaves.

Figure 1.5. Large amount of dead leaves

dropped at the end of summer.

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is continued all the year round, it is more intense

from August, when it is possible to say that the fall

begins (Fig. 1.5), being with the big autumns

storms with the maximum loss of leaves will take

place. The same storms drag up to the coast the

fallen leaves, forming they typical accumulations

on the beaches, called “banquettes” (Calvo 1995)

(Fig. 1.6).

Being a real plant, P. oceanica produces flowers, but does it rarely. Usually, less than 1 flower

is produced per 10 square meters per year, but flowering may be more frequent during warm

years (Borum 2004). The flowers are hermaphrodites and are grouped in inflorescences that

arise in the center of the bundle, which impedes its

observation (Fig. 1.7). The pollen forms viscous

filaments that drift. The fruits of P. oceanica have the

shape and the size of an olive; they are generally dark

green and have just one seed (Hartog 1970). They

require 6-9 months to ripen. Between May and July,

they drop off and float for a certain time. According to

the direction of the currents, they may be washed up on

beaches in great quantities. However, P. oceanica

reproduces mainly in a vegetative way; this

reproduction strategy is called “stolonization”, and

occurs by dispersion of rhizome fragments and its

horizontally increasing by producing lateral

ramifications.

P. oceanica’s low genetic variability could be a weakening factor for this species (Raniello et

al., 2002). The rarity of the flowering and, especially, seed production, as well as self-

pollination, and inversely the frequency of vegetative reproduction could explain this feature

of low variability. The little investment and low success of sexual reproduction, combined with

the extremely slow clonal spread of P. oceanica explains the extremely slow colonization rate

of this species. Numerical models simulating the occupation of space by P. oceanica meadow

suggest that it would need 600 years to cover 66 % of the space available. Similar colonization

timescales have been calculated based on patch size and patch growth rate in patchy P. oceanica

Figure 1.6. "Banquettes" formations along La Fossa

beach, Calpe.

Figure 1.7. P. oceanica flower phases: (1)

apariencia, (2) ovule formation and several

dehiscent anthers, (3) fertilized ovule, (4) seed,

germinating producing first leaves, small rhizome

and a root to be fixed to the sediment.

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meadows. The very long time scales for colonization of this species indicate that recovery of

disturbed P. oceanica meadows, where important plant losses have occurred, would involve

several centuries (Borum 2004). P oceanica is a long-living seagrass, with shoots able to live

for at least 30 yr P. oceanica recruited shoots at low rates (0.02 to 0.5 In units yr-1) which did

not balance the mortality rates (0.06 to 0.5 In units yr-1) found in most (57 %) of the Spanish

meadows. If the present disturbance and decline rates are maintained, shoot density is predicted

to decline by 50% over the coming 2 to 24 yr. Because P. oceanica rhizomes grow very slowly

(1 to 6 cm yr-1), maintenance of existing meadows is essential, and our results suggest bad

future prospects for P. oceanica in the Spanish Mediterranean Sea like most other seagrass

species in the world oceans (Marbà et al., 1996).

1.4 Ecology

In calm conditions, P. oceanica can develop very near average sea level: its leaves then spread

out on the surface, while the maximum depth depends on water transparency. In fact, light is

one of the most important factors for the distribution and density of P. oceanica regulating the

lower depth distribution (Elkalay et al., 2003).

P. oceanica dislikes low salinity. It dies off immediately below 33 ‰. The species appears to

resist high salinity levels more successfully, although Ben Alaya (1972) has shown that 41 ‰

constitutes its upper tolerance limit. In fact, for example, it is present in the hypersaline lagoons

of Tunisia (Bahiret el Biban, 46‰ in August) and Libya (Farwa: 39-44‰ according to the

season); in these lagoons its vitality, as number of leaves produced per year, seems identical to

or above what is observed out at sea (Romero et al., 1992, Pergent et al., 2000).

The extremes of temperature measured in a P. oceanica meadow are 9.0 and 29.2°C (Augier et

al., 1980). It is, however, possible that low and high temperatures are only exceptionally borne.

P. oceanica’s absence from the Levantine coast and its scarcity in the northern Adriatic could

be due respectively to the summer and winter temperatures. Also, in deep meadow, Mayot et

al., (2005) suggest that the increase in seawater temperature that is currently observed, could

have a harmful effect on this seagrass. The temperature is therefore considered the overall

parameter controlling the geographical distribution of the species in Europe.

Moreover, P. oceanica dislikes too intense hydrodinamism, and exposure is the most important

factor regulating the upper depth distribution of a meadow. In general, it is estimated that

9

seagrasses do not exist at flow velocities above 1.5 m per second or at very exposed shores.

Currents and wave action prevent seagrass growth and distribution by causing resuspension and

transport of the sediment. Besides affecting the general light climate of the water column,

erosion can expose roots and rhizomes causing the seagrasses to detach from the sediment.

Additionally, very strong currents or wave action may tear up entire plants or prevent new

shoots from being established (Borum 2004). Storms tear off shoots and can also erode the

“matte”, either directly, or by leaching the sediment, which weakens the meadows. That is why

in rough sea conditions the meadow grows no nearer the surface than 1 or 2 meters.

1.5 Structure of meadows

Seagrasses deeply alter the environments they colonize, giving rise to specific systems, known

as the most diverse, complex and productive meadows present along the coastal zone of almost

all the oceans and seas (Short and Coles 2001). The leaves and rhizomes of P. oceanica support

many flora and fauna, some of which are calcified. When they die, their remains fall off and

form an autochtonous sediment. Moreover, because of their density and distribution, the leaves

of P. oceanica reduce the speed of the current; this reduces the kinetic energy of the sedimentary

particles carried by the water, which then deposits on the seabed, constituting the allochthonous

sediment (Boudouresque 2012).

P. oceanica rhizomes grow in height, even in the absence of sedimentation. To resist being

buried, they are capable of speeding up their growth (Boudouresque et al., 1994).

The “matte” is the whole mass composed of rhizomes, leaves, roots and the sediment that fills

the interstices. All complex is not very putrescible and is conserved for several centuries or

even thousands of years (Boudouresque et al., 1983). Over the course of time, the “matte” rises

to the surface, Moliner and Picard (1952) measured a seabed elevation of 1 meter per century.

The “matte”’s elevation, in some conditions, can reach the surface, forming a barrier reef.

1.6 The role of Posidonia oceanica meadows in coastal systems

1.6.1 Ecological role

Darwin (1859) was the first to say that marine seagrasses can constitute a food base for many

species of macro-herbivores.

10

As with forests in the terrestrial environment, P. oceanica meadows are the climax community

and their presence attests to a relatively stable environment. In numerous Mediterranean coastal

water ecosystems, P. oceanica plays an important role in a number of key geomorphological

and ecological processes such as nutrient recycling (reducing the degree of water movement,

thus improving sediment stability), provision of food for herbivorous fauna, shelter and nursery

areas for many organisms (e.g. fishes, crustaceans) (Francour et al., 1999). These meadows are

also a unique biodiversity hotspot (Boudouresque 2004).

Just inside the meadow it is possible to distinguish two populations: one photophilous and

adapted to the expiration of the leaves on which it is installed, and another sciophilous and more

stable installed in the stems and

rhizomes. The leaves are occupied by

small species of epiphytes (Fig. 1.8), of

very short life and very fast crescent,

which are adapted to the rapid and

particular growth of the substrate in

which they are fixed. In the rhizomes,

propriate species of the rocky bottoms

are installed. Thus, if the density of the meadow is high, the light that reaches the rhizomes is

scarce and the species that appear belong to the precoraligenous community or the sciaphilic

algae of calm regime, whereas if the density is low, the light that arrives at the rhizomes is

enough so that the species of the infralittoral photophilic algae community can calmly settle

down. In the buried part of the rhizomes, a typical fauna of soft bottoms is installed, rich in

bivalves, polychaetes and small crustaceans.

A basic feature of the P. oceanica ecosystem is the

combination of two kinds of primary production; at global

level, only marine seagrasses ecosystems present this special

feature (Boudouresque et al., 1996). (1) The primary

production from P. oceanica is rich in cellulose and lignin,

compounds that are not used much by herbivores, and in

phenolic compounds, one of whose roles is to dissuade

potential consumers. The net primary production of P.

oceanica is on average between 420-13000 g DM/m2/year

(DM = dry mass); it drops in relation to depth (Pergent et al.,

Figure 1.9. Production processes

(Boudouresque et al. 2012).

Figure 1.8. Dense epiphytic community on P. oceanica leaves.

11

1997). (2) The primary production from the Multicellular Photosynthetic Organisms (MPOs)

leaf epibiota is composed of very palatable Rhodobionta and Chromobionta, thus easily usable

by herbivores; it is between 100 and 500 g DM/m2/year (Giorgi and Thelin 1983). All in all,

the P. oceanica ecosystem is one of the planet’s most productive ecosystems (Boudouresque

2012). Vegetal biomass is also very high and decreases with depth (Mazzella et al., 1992). No

other marine ecosystem, except mangroves, presents such high vegetal biomass. This is due to

the storage of the biomass over a long period of time in the “matte”. Little (less than 10%) of

the primary production is used by herbivores. These are mainly the fish Sarpa salpa (Fig. 1.10),

the sea urchin Paracentrotus lividus, isopod crustaceans Idotea hectica, spider crabs Pisa

mucosa and P. nodipes (Boudouresque and Verlaque 2001). The modest grazing role of S. salpa

could constitute an artifact linked to human

action; indeed, in a certain number of Marine

Protected Areas (Tabarca and Medes Islands in

Spain, Port-Cros in France, El Kala in Algeria)

overgrazing by S. salpa was observed

(Boudouresque et al., 2012). On the other hand,

the leaf epibiota is widely used, in particular by

gastropods. Much of the primary production (24

to 85 %) is exported in the form of dead leaves;

they may constitute up to 40% of the digestive contents of sea urchin P. lividus in a hard

substratum community some hundreds of meters away from the nearest meadow (Cebrian and

Duarte 2001).

Figure 1.11. Meadow patch with clear signs of herbivorous S. salpa.

Figure 1.10. Individuals of S. salpa grazing on P.

oceanica.

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1.6.2 Physical role

On the coastal seabed, P. oceanica meadows are real plant barriers that encourage the

decantation and sedimentation of particles in suspension in the water column (trapping

sediment) (Fig. 1.12). The meadow plays a

similar role to European beachgrass and pine

trees that stabilize the coastal sand dunes. It

should also be noticed that sediment settling

and trapping in the “matte” increase the

transparency of the coastal water

(Boudouresque and Meinesz 1982). The P.

oceanica meadow’s considerable vegetal

biomass also acts as a kind of barrier which

slows and effectively absorbs hydrodynamism at the seabed. Some experiments in laboratory

and in situ showed that a meadow can reduce hydrodynamism from 10 to 75% the under the

cover of leaves and 20% above the canopy (Gacia and Duarte 2001). This hydrodynamism

reduction is particularly visible behind the P. oceanica barrier reefs, where the presence of these

plant barriers enables sheltered lagoons to be established (Boudouresque et al 1994) and more

generally the reduction in waves and currents is likely to protect from coastal erosion and helps

stabilize the shoreline.

1.6.3 Economical role

It is the result of the ecological and physical importance in the coastal system. It obviously

affects the management of living resources via its high biological production, the protection

from predators it offers to young fish and young organisms, and it also continues a much sought-

after spawning ground for many species of commercial interest (Connelly et al., 2005). It also

affects the development of tourism and seaside activities, by helping maintain water quality,

and especially by stabilizing the shoreline that it defends by protecting it from erosion.

Furthermore, even if the meadows are not always the “spots” sought by divers, they are at the

origin of significant exported biological richness (in terms of species and food) to other more

sought-after habitats (Boudouresque 2012). Moreover, P. oceanica leaves dead can be very

useful. Use of the leaves inside mattresses, or as bedding for animals, went on for a long time;

indeed, “vermin” never entered the mass, certainly because of the phenolic acid contained in

Figure 1.12. Physical role of P. oceanica meadow, modified from

Bourdouresque and Mainesz. (1982).

13

the leaves (Bourdouresque et al., 2012). For centuries, when there was not yet any bubble wrap

or expanded polystyrene, P. oceanica leaves were used by the Venetians to wrap up and

transport their famous, delicate glasswork, to the extent that these leaves were known as

“Venetian straw”. In North Africa, in the early 20th century the coastal populations were still

using dried P. oceanica leaves to build roofs, while in Corsica, Sicily and Greece these were

used for thermic and sound insulation. Dead P. oceanica leaves were also used for a long time

as compost by farmers on the Mediterranean coast.

1.6.4 Bioindicator role

For several years now, the use of seagrasses for environmental monitoring, to assess the

evolution of impact, or more generally to manage coastal ecosystems has been envisaged. The

use of these species, known as “bioindicators”, seems to be a quick and effective way of

assessing the quality of the environment (Bellan 1993).

Seagrasses in general, and P. oceanica meadows in particular, are considered to be appropriate

for biomonitoring because of their wide geographical distribution, reasonable size, sedentary

habit, longevity, permanence over the seasons, easy collection and abundance and sensitivity

to modifications of the littoral zone. Reasoned management, on the scale of the whole

Mediterranean basin, requires standardized methods of study, to be applied by both researchers

and administrators, enabling comparable results to be obtained (Pergent-Martini et al., 2005).

In particular, P. oceanica meadow constitutes a powerful integration of overall marine water

quality, it demonstrates by its presence and its vitality the quality of the water above it.

Moreover, their rhizomes concentrate radioactive, synthetic chemicals and heavy metals,

recording the environmental levels of such persistent contaminants.

In summary P. oceanica seems to be a reliable bioindicator according to: (1) their sensitivity to

disturbances, as demonstrated by a number of reports of meadow regression due to various

causes; (2) its wide distribution along the Mediterranean coast and (3) the good knowledge

about specific response of the plant and of its associated ecosystem to specific impact (Tab.

1.3). Furthermore, as said, this species is able to inform about present and past level of trace

metals in the environment (Pergent-Martini, 1998).

14

Moreover, P. oceanica meadows, from a political point of view, are included in a law issued at

European level. In fact, the use of seagrasses as a tool for an ecological evaluation of coastal

waters has recently been highlighted in European legislation by the Water Framework Directive

(WFD 2000/60/EC). The Directive establishes the basis for monitoring, protection and

enhancement of all aquatic ecosystems in the European Member States (MS), by setting

ecological quality objectives (i.e. ‘‘good water status’’ for all European waters by 2015) which

require to assess water quality status using a combination of ecological indicators in priority.

To assess the good status of water bodies, the WFD requires that monitoring programmes are

Table 1.3. List of main descriptors of P.oceanica used in monitoring and their

responses to different impacts, 1: community descriptors, 2: individual

descriptors, 3: physiological descriptors (Pergent-Martini et al., 2005;

Boudouresque et al., 2006; Romero et al., 2007).

15

implemented for the ensemble of aquatic environments concerned. This monitoring must be

based on “biological quality elements” (BQE). For coastal waters Angiosperms, together with

phytoplankton, macroalgae and benthic fauna (Devlin et al., 2007), are one of the four BQEs

required for the evaluation of ecological status because of, as mentioned above, its specific

responses to anthropogenic disturbance are acknowledged (Balestri et al., 2004; Ruiz and

Romero, 2003; Leoni et al., 2006).

Using some descriptors, have been therefore elaborated, from the scientific community, a series

of indexes (Tab. 1.4), on the P. oceanica metrics, so that the evaluation of the quality of the

waters can be simple, replicable in space and time, and can have a reasonable cost.

Recently, in addition to the plant itself, the composition and abundance of the leaves epiphytic

community is beginning to be used as a BQEs. In fact, the deterioration of the water quality and

the increased amount of dissolved nutrients, due to the rising human pressure on coastal waters

in the last century (UNEP/GPA, 2006), have been shown to affect the growth of epiphytes on

seagrass leaf blades (Duarte, 2002). Increases in the epiphyte biomass, differences in their

spatial heterogeneity and shifts in species composition have been observed under human

disturbance regimes. Moreover, differently from the descriptors commonly adopted for

Table 1.4. Three methods based on Posidonia oceanica in the WFD to assess the ecological status of

Mediterranean coastal waters (Gobert et al. 2009).

16

evaluating the health status of P. oceanica ecosystem, the epiphyte community structure was

able to detect alterations in the water quality already after 4 months (Giovannetti et al., 2010).

1.7 The causes of regression

Seagrass communities, which are widely considered as key ecosystems in coastal waters (Short

et al., 1996), are now challenged with hasty environmental alterations resulting from human-

induced disturbance (Boudouresque et al., 2006). Worldwide seagrass loss has been reported

due to a variety of both direct and indirect human impacts (Short et al., 1996; Hemminga et al.,

2000). In the Mediterranean Sea, the major sources of large-scale seagrass regression include

environmental pollution, eutrophication, increased water turbidity, bioinvasion, and climate

changes (Montefalcone et al., 2007; Occhipinti- Ambrogi, 2007), but there are also sources of

regression of little-scale.

When water transparency decreases this has a direct effect on P. oceanica meadows.

Compensation depth (the depth at which the losses due to respiration balance out with

photosynthesis production) becomes shallower, and with it becomes shallower the limit of the

meadow. Ruiz and Romero (2001) have demonstrated experimentally, placing screens above a

meadow, that a reduction in light reduces both growth rate, shoot biomass and storage of starch

in the rhizomes; and after one year, when normal light intensity has been restablished there is

still no sign of recuperation.

For example, a harbor construction or building coastal facilities can locally change swells and

currents and alterate the normal sedimentation dynamic (erosion or accumulation). All that can,

consequently, cause a clear increase in sediment organic matter and in sediment deposition

rates, especially fine sand. For this reason, light availability could be reduced due to suspended

sediments. Seagrass structural indicators respond unequivocally to these environmental

changes, with clear reductions in shoot density (Roca et al., 2014).

Also coastal rivers can have an impact on P. oceanica meadows by: desalination to which the

plant is very sensitive, nutrient and sediment inputs. The correction of watercourses can modify

the granulometric features of the sediment carried down in favor of the finest particles,

generating great turbidity in the water column which restricts the photosynthetic action of P.

oceanica.

17

Also nutrient inputs resulting from fish farming activities located in the vicinity of seagrass

meadows can potentially alter the structure and affect the functioning of these ecosystems. The

presence of suspended matter in the water column can cause a reduction in the amount of light

reaching the seagrass, while elevated concentrations of dissolved nutrients can promote a high

epiphytic cover on the leaves. The overall result is a reduction in growth rate of the seagrass

and gross changes in shoot morphology (Dimech et al., 2002). In a particular way, Cabaço et

al., (2013) showed that biomass and density tended to increase simultaneously under high

nutrient levels in short-term experimental studies, whereas they tended to decrease

simultaneously in descriptive studies where the seagrass populations were exposed to the long-

term effects of nutrient increase.

Anthropogenic waste, as well ad greatly changing the sedimentary balance of the coastal water,

also implies a wide range of contaminants that affect the vitality of the P. oceanica meadows.

The effect of soluble substances is rapid, but insoluble substances can also have a very negative

impact; being relatively stable they can accumulate to reach concentrations that are toxic to

flora and fauna. The presence of a high contaminant concentration can determine the alteration

of the biosynthetic pigments: along with an increasing pollution gradient, the photosynthetic

pigment content in P. oceanica leaves decreases (Augier et al., 1979).

Moreover P. oceanica meadows, ranging in depth from the surface down to about 40 m, cover

seabed areas that coincide with the ideal sites for pleasure- boats anchoring (Montefalcone et

al., 2008). Among the various types of human activities, the mechanical damages resulting from

uncontrolled pleasure boats anchoring (Fig. 1.13) in

shallow coastal waters would appear to be responsible for

localized regressions of P. oceanica meadows

(Montefalcone et al., 2006). The impacts of anchoring

systems on P. oceanica have been shown to be recorded at

two different levels: the individual level (the plant), where

mechanical damage is the direct cause of pulling up leaves

and rhizomes (Ceccherelli et al., 2007), and the population

level (the meadow), where mechanical damage reduces

shoot density and cover of the meadow (Francour et al.,

1999). Experimental evaluations of the impact of anchors

of small vessels have shown that each anchoring can on

average damage up to 6 shoots of P. oceanica, removing

Figure 1.13. Impact of an anchor of leisure

boat on P. oceanica meadow.

18

small amount of biomass and, at the same time, interrupting continuity among shoot, and the

disturbance is higher where the substratum is highly penetrable (Ceccherelli et al., 2007). The

frequency of anchoring at some visited sites, in terms of number of boats and extension of the

visitation period, could make this chronic disturbance very stressful to the growth of the

seagrass over several years; compared with the slow clonal growth of P. oceanica, estimated at

about 1–7 cm yr−1, recovery may take centuries. Notwithstanding the protection measures

undertaken by the European Community for their conservation, P. oceanica meadows keep on

being affected by this kind of local impacts, which are hardly controlled but within marine

protected areas (González- Correa et al., 2007). An alternative to direct anchoring is the

deployment of anchoring chain systems to which buoys – and subsequently boats – are moored

(Montefalcone et al., 2008).

Another cause of regression of the P. oceanica meadows is the competition with two

Chlorobionta introduced species: Caulerpa taxifolia and C. racemosa (cylindracea). C.

taxifolia and cylindracea are native to Australia and were accidentally introduced into the north-

western Mediterranean at the beginning of the 90’s, since when its geographical expansion was

relatively rapid. C. taxifolia is able to colonize almost all kinds of substrate, particularly the

“dead matte”, so stressed and degrades meadows are an extremely favourable environment for

this species (Boudouresque et al., 2012), while C. cylindracea colonizes bottoms bordering P.

oceanica, and its growth in height is a function of the P. oceanica shoot density and the

orientation of the meadow (Ceccherelli et al., 2000).

It is not always easy to distinguish between natural and human factors, or between the different

kinds of human-induced factors, which almost act simultaneously and certainly have synergic

effects, should not hide a robust scientific certainty: man really has been responsible for most

of the regressions observed in the second half of the 20th century.

1.8 Policies applying to Posidonia oceanica meadows

For all the reasons mentioned above and due to the fact that P. oceanica meadows have great

short-term recovery difficulties, this led to enhanced efforts in protecting legally the species in

many Mediterranean countries (Platini 2000).

19

It is useful differentiate between direct legal protection measures either concerning the species

P. oceanica or the habitats it constitutes, and regulatory measures which, without directly

aiming to protect the meadows, can indirectly encourage their conservation.

In policy terms, the ecosystem approach is a relatively recent one and only international

conventions signed after 1990, or those were produced before this date but were updated,

possibly take P. oceanica meadows into account. This is the case of the Bern Convention

(Convention on the conservation of European wildlife and natural habitats), signed in 1979

under the auspices of the Europea Council by several Mediterranean countries. Indeed, while it

did not initially mention any marine plant species, its Annexes were modified to add three of

the seagrasses species of the Mediterranean Sea (Cymodocea nodosa, Posidonia oceanica and

Zostera marina). The same holds good for the Barcelona Convention, adopted in 1976, which

was the key convention for the protection of the areas and species in the Mediterranean. A legal

tool of the Mediterranean Action Plan (MAP), launched by the UNEP (United Nations

Environment Programme), for the protection of regional seas, the convention initially focused

on the marine pollution, but in 1982 the 20 signatory countries showed their interest in

protecting marine habitats adopting the Mediterranean Specially Protected Areas Protocol.

However it was only in 1999, when a new protocol was adopted, that P. oceanica is specifically

mentioned in a list of endangered or threatened species and also the ecosystem that it built is

recognized of “special interest at the scientific, aesthetic, cultural or educational levels”, and

then introduced in the SPAMI (Specially Protected Areas of Mediterranean Importance) list.

These provisions were enhanced when in October 1999 and Action Plan for the conservation

of marine vegetation in the Mediterranean was adopted. It identifies priority actions at national

and regional level, such as ensuring the conservation of species and plant formations by

developing legal measures of protection, avoiding the loss and degradation of marine meadows

and of other plant formations and habitats for marine species, and ensuring the conservation of

formation as P. oceanica barrier reefs, considered natural monuments.

To these international conventions should be added the Habitats Directive of 21 May 1992

(92/43 EEC/Natural Habitats), at European level. This Directive has six Annexes, and in the

first one appear the P. oceanica meadows which are classified as a priority habitat.

Several countries now have specific laws about meadows or envisage such procedures, if only

to make the provisions mentioned in the international conventions they have signed or ratified.

20

For what concerns indirect ways to protect marine meadows is possible to recall all the policy

measures that aim at restricting pollutant waste, ensuring the treatment of urban waste, fighting

against water eutrophication, banning certain fishing techniques and fighting against the

introduction of invasive species. Also setting up Marine Protected Areas can be a way of

protectin P. oceanica meadows even if conserving spaces do not specifically refer to the

meadows.

21

2. Work purpose

The main purpose of this work is, through a first survey, to provide baseline data for the

monitoring scheme of Posidonia oceanica meadows at Calpe Bay. The features and status of a

seagrass bed have been assessed by physical, physiographical, structural and functional

descriptors.

22

3. Materials and methods

3.1 Study area

This study was carried out in the waters of the “Parque Natural del Peñón de Ifach”. Ifach's

Crag (Penyal d'Ifac in Valencian) is located in the region of the High Sea-coast in Calpe's

municipality in the province of Alicante (Spain) (Fig 3.1).

The Crag is 332 m above the sea level and has an area of 50.000 m2 (Fig. 3.2). This calcareous

mountain was declared Nature reserve by the Decree 1/1987, January 19, of the Valencian

Government. Only in 1993 has definitely been approved the plan of management of the park

that currently extends for a total of 53,3 acre and it is entirely terrestrial. The surrounding marine

area to the mountain has recently been declared special protection area (SPA) under the Birds

Directive (79/409/CEE), while no protection plans have been implemented for the marine area.

On both sides of the natural reserve, there are opened beaches of thin sand: "Levante" or " La

Fossa " towards

North; “Cantal

Roig” and

“Arenal‐Bol”

towards South,

which, together

with "Morro de

Toix", shape the

coastline of

Calpe's bay (Fig.

3.3).

Figure 3.1. Geographic location of the study area. Figure 3.2. View of the Peñón de Ifach from the sea.

Figure 3.3. Calpe bay from above.

23

3.1.2 Geological context

Ifach's Crag is the last spur of the Baetica mountain chain (Andalusia) and is part of the internal

delimiting of the mountain chain called Prebética. The compressive efforts in the Prebetic sector

formed the basin that was refilled by Miocene’ marine materials among those who inserted big

fallen blocks (olistoliths) proceeding from the top part of the folds of Oltà's Saw. The olistolith

of Ifach's Crag (limestones eoceno-oligocenas) finished resting on the younger miocenas marls.

In the Eocene - Oligocene, approximately 65 millions of years ago, the place that today occupies

the Crag, was a marine slightly deep platform in which were going settling the remains of

fossils. 14 million years ago an intense orogenic phase took place forming big faults of

orientation, responsible for the collapse under the sea of the sectors placed between Morro de

Toix and Ifach's Crag. In addition, big blocks of land emerged to the surface (olistoliths). The

most recent materials are a consequence of the coastal deposition in conditions of marine slow

and continued regression, these are dune cords that do not appear on the surface. The crag is

joined to the continent by a detrital isthmus, which is a sedimentary environment recent littoral.

Approximately two million years ago, the sediment proceeding from the rivers and from the

erosion of the cliffs formed a tongue connection for the action of the coastal dynamics (Fig.

3.4). Between the island and continent there existed a slightly deep strait that went away for

sandy contributions brought by the currents parallel to the coast, giving origin to two sandy tops

of the coastal arrow (now cemented sandstones). At the same time the wind action accumulated

contributing materials forming a

dune cord that isolated in the interior

a zone flooded with salt waters,

result of the mixing of continental

waters with the sea. Therefore the

Salt mine is a part of a former bay

closed by the formation of this

transverse cord dune to the surge.

Nowadays it is possible to see this

barrier of fossil dunes between

Arenal and Cantal Roig beach.

Another part of the barrier would be

in the La Fossa beach. Figure 3.4. Formation process of the Salt mine and the isthmus that

connects the Peñón de Ifach to the land (from García-March et al., 2015).

24

3.1.3 Marine context

The seabed adjacent to the mountain is very heterogeneous in relation to the mountain

orientation (Fig. 3.5).

The depth gradient is really marked in the south/southwest zone of the Peñón de Ifach, where

it quickly reach -35 m. On this side of the mountain, there is a beach of pebbles (Racò Bay)

along the depth gradient gives gradually step to different biocenosis of thin sands. On this side

of the cape, a great P. oceanica meadow is present, which extends from -6 m to -22 m depth.

The sector north of the Peñón de Ifach, however, has vertical walls at the base of which great

calcareous blocks are located coming from the detachment of the walls of the same mountain.

On this side, there is a really big sandy beach (La fossa beach) beginning from which the sea

floor goes deeper very slowly. From this side of the mountain, there are two different meadows

of P. oceanica, one directly in front of the beach constituting a structure like a reef, while the

other is situated on the north slope of the mountain.

The waters that surround the Peñón de Ifach are protected from wind and surge principally in

his west and north faces due to the geographical protection that he is awarded by the saws of

Oltá, Bernia and Mascarat. In turn, the sectors south and North-East are the most exposed to

climatic phenomena of this type being the most frequent proceeding from this side.

The whole area is affected by a variety of anthropic pressures, most of which are related to

tourism. From June, the number of tourists that reach the area and that consequently crowd the

beaches, reaches exorbitant numbers. Also the number of boats that anchor in the bays increase

Figure 3.5. Bottom batimetry from Marinetraffic.com.

25

very much in summer, going to constitute a probable threat for the P. oceanica meadows, also

because there are no buoys to attach to, instead of anchoring.

Behind Cala Racò bay is located a fishing port that does not directly affect the area, but has

done it in the past. The fishermen comment that up to a couple of decades containers did not

exist to throw the garbage in the

fishing port and that the garbage

of major size, gathered by the

trawlers, was beginning to be

thrown into the Cala Racò area,

the so-called “Brut de Ifach”

(García-March et al., 2015) (Fig

3.6). In this way, for many years

there was spilled all kinds of

residues of large size, from ropes

up to girders, containers and

fishing tackles. Some remains have joined the bottom and on them, numerous incrusting

organisms and P. oceanica have grown, but the majority perceive it as a problem from the

environmental and aesthetic point of view. It would suit to solve by means of a professional

cleanliness of the funds, coordinated with scientists, to minimize the ecological impact of the

own extraction of the garbage.

3.2 Physical descriptors

3.2.1 Water conditions

To monitoring the physical-chemical parameters of the water, such as

temperature, turbidity and dissolved oxygen a

multi-parameter CTD probe has been used,

AAQ-RINKO (LFE Advantech Co., Ltd.) (Fig.

3.7). It is connected, through a cable, to a hand-

held unit that records the measured parameters,

returning the profiles along the water column.

Figure 3.6. "Brut de Ifach" mapping from García-March et al. (2015).

Figure 3.7. CTD probe and console.

26

Conventional water quality profilers with a

slow response optical sensor require holding

the instrument for a certain period at the

measurement depths. The one we used, with

an optical fast response, makes vertical

measurements possible with a profiling speed

of 0.5 m/s, thereby significantly reducing the

observation time.

The data were collected once a month, for one year, up to -30 m depth, to have information

related to the whole range in which the meadow of P. oceanica is distributed.

3.2.2 Sediment analysis

From October 2016, samples of sediment of around 300g were collected monthly, in three

different stations (C01 -5m, C02 -10m, C03 -15m) of the Cala Racò meadow (Fig. 3.9.), with

the purpose to analyze its particles size and to quantify in its variation in relation to the seasons,

related to hydrodynamic conditions.

Figure 3.8. CTD probe sensors.

Figure 3.9. Sediment monitoring station in Cala Racò meadow.

27

To do so each sample has previously been prepared: rinsed with

distilled water to avoid that the crystals of salt created adhesion among

the grains and they brought to a distorted result. Subsequently to this

step, the samples were set in heater for at least 24 hours to 70°C. A

special battery of sieves (CISA) was used, in which the mesh size

decreases downward progressively, reducing itself of ½ every level

(Fig. 3.10). The whole battery was placed on a mechanical agitator

(CISA sieve shaker Mod. RP08 (Fig. 3.11)) for a period of about 30

minutes, with the purpose to get the complete sifting of the material.

Subsequently, every fraction held back

inside every sieve appraising was weighted

and the percentage of it in comparison to the

total weight for every single granulometric

class of affiliation was calculated. The

values of every single weighed so gotten are

reported to the classes belonging on the Wentworth’s scale. All the

sediment samples were analyzed fresh, whereas it was not possible,

they were frozen with the purpose to maintain their integrity.

Since granulometric distributions can be assimilated to Gaussian curves,

the dimensional spectrum description follows the rules of classical

statistical parameters. These "classics" can be integrated by a different

index, which can be revealed graphically or by analytical methods from

cumulative curves. These curves were constructed by adding each size

class to the previous one, on the abscissa there were the values of the sieve

diameter on a logarithmic scale (ø notation = - log2(mm), Tab. 3.1).

From these curves, after calculating the values for the percentiles, it was

possible to obtain the descriptive parameters (Folk and Ward 1957).

mm ø

notation

2

1

0.5

0.25

0.125

0.063

<0.063

-1

0

1

2

3

4

5

Table 3.1 Conversion

scale from mm to ø

Figure 3.10. Sieves

illustration and relatives and

dimension of the holes.

Figure 3.11. Agitator and sieves

photo.

28

NAME MEANING FORMULA (Falk & Ward 1957)

Mdø Average diameter.

σ

Sorting or standard deviation of the

sediment, represents the measure

of dimensional variability within

the sample. It gives information

about the sediment classation.

Sk

Skewness, it represents the

measurement of distribution

symmetry. The values can range

from -1.0 to +1.0. It provides

information on the energy to which

the sediment is subjected, and

hence to the relationships between

the dimensional classes that make

it up.

K

It represents the measure of the

slugness of distribution in relation

to sorting. This parameter has a

poor geological significance.

Fh

Hydrodynamic factor, allows

estimating the mean value of the

currents.

Table 3.2 Folk & Ward parameters and their meaning.

29

3.3 Monitoring Posidonia oceanica

Six monitoring stations were realized, four of which located in a single meadow on the South

slope of the Peñón de Ifach mountain, and two situated in lists stains on the North side of the

same mountain (Fig 3.12).

Every station of monitoring consisted of 6 points of sampling, in each of which a SCUBA diver

team realized the corresponding measurements, along a transect 10 meters long (Fig 3.14).

The position of every sampling point were indicated by a metallic picket of 1,5 m of total length,

fixed in the sediment and provided with a small buoy that stands out 1 meter above the leaves

(Fig 3.14).

Figure 3.12. P. oceanica monitoring stations.

Figure 3.13. Members of the SCUBA diver team.

Figure 3.14. Schematization of the structure of a sampling station.

30

The pickets were numbered and distance between two adjacent

pickets ranged between 3 and 6 meters (Sandulli et al., 1998),

following the limits of the meadow, when presents, so that they

could be used as reference for the monitoring regarding the

expansion or the regression of the limit of the meadow during the

years. The examples brought in literature to monitoring the lower

limit of P. oceanica meadows foresee the use of bodies of reference,

e.g. blocks of cement or metallic rods, that don't have the possibility

to be moved by the hydrodynamic action (Buia et al., 2003). For

each transect, the direction (in °) was recorded, in this way, every

measurement can be repeated in the same place, at the time. The

majority of the stations were located in correspondence to the lower

limit of the meadow to show, eventually, first signs of degradation of the system. The typology

of border has been defined following the classification of Meinesz and Laurent (1978) and

Pergent et al., (1995).

Furthermore, for each meadow (A, B and C) it has been classified the Bed typology that together

with the Limit typology constitute the physiographical descriptors of seagrasses meadows.

The ecological status of the P. oceanica meadows was assessed investigating some structural

descriptors:

- Shoot density: is the number of seagrass shoots m-2 and thereby provides a measure of seagrass

abundance along depth gradients. This descriptor was measured along every single transect

three times, for a total of 18 measures each station, using a 25x25 cm PVC frame. These values

were reconducted to a square meter. This variable represents one of the most important

descriptors to appraise the status of a meadow, above all if measured on a multiannual temporal

scale (Buia et al., 2003).

- Covering: is a measure of abundance, but expressed as a percentage. It consists in visual

estimation of the percentage of the surface of the bottom occupied by the shoots of P. oceanica

on a known area. Ten measures of this variable were conducted on each transect (one each

meter), for a total of 60 measures in every station, using a 40x40 cm PVC frame. To facilitate

the sampling, frames were subdivided into 4 subsquares of 25x25 cm. To each subsquare a

value ranging from 0 % to 100 % was assigned according to the proportion of surface that was

Figure 3.15. Reference buoy

connected to a picket.

31

occupied by the shoots (Fig. 3.16). All measures were done by two previously inter-calibrated

operators.

From these two descriptors the Global density was estimated as the result of the product of the

average density inside P. oceanica patches and the proportion covered by the meadow (Romero

1985).

- Burial: it is the vertical distance (in centimeters) between the level of the sediment and the

ligule of the most external leaf of the shoot of P. oceanica. The value and sign of this distance

changes depending on the balance among the vertical growth of the plant and the dynamics of

the sediments in every site: it is positive (sediment level below the ligule line) if erosion

processes are predominant, and negative (sediment level above the ligula) if an excessive

accumulation of sediments exists on the meadow. The burial of the vertical shoots of P.

oceanica then is a symptom of erosion of the meadow. Both the erosion and the deposition of

sediment provokes an increase in the mortality of shoots of the meadow (Cabaço et al., 2008).

The meadow to be healthy, the sediment must be stable or accumulate at low rates, so that the

meadow could respond with an elevation rate of the substratum of few cm year-1 (Gacia and

Duarte 2001). High rates of sediment deposition provoke the burial of the meadows.

Accumulations of sediment superior to 10 cm provoke the mortality of shoots of 50 %, and

when the burial of the rhizome exceeds 14-15 cm, the mortality of shoots is 100 % (Cabaço et

al., 2008). To evaluate the burial of the shoots on the selected stations, the vertical distance (in

centimeters) between the sediment and the lígula (meristem of growth) was measured in one of

Figure 3.16. Estimate of Covering structural descriptors of the P. oceanica meadow, along a transect of 10 m length (Marbà

et al. 2015).

32

the external leaves of the bundle of P. oceanica. In every station these measures were realized

12 times each transect.

Furthermore, in each station 30 shoots were collected to proceed with the analysis of the

morphology of the leaves. In this case, the functional descriptors analyzed were:

-Number of leaves/shoot

-Leaves length

-Leaves width: measured around the middle of the leaf.

-Apex status: it can appear entire, broken or bitten from some herbivorous. It can be

distinguished from the shape like in Figure 3.17.

From this synthetic descriptors can calculate the derived descriptors. They are:

- Leaf area average for shoot (cm2 shoot-1): for every shoot, the surfaces of all the leaf (an only

face is considered) edges are calculated, therefore the gotten values are added for having the

total area of the shoot and they are finally mediated for the number of sampled shoots.

- Herbivorous rate: how many leaves result vices herbivorous on the total one, directly derived

from the analysis of the apex status.

- Leaf Area Index (m2 m-2): it is calculated multiplying the surface leaf average for shoot for

the density of the meadow for each square meter.

- Coefficient "A": percentage of adult and intermediary leaves that has the apexes broken; it is

calculated dividing the total number of adult and intermediary leaves with broken apexes for

the total number of the observed leaves. The value of the coefficient "A" it is more often the

result of some factors like the hydrodynamism, the age of the leaves and the level of presence

of herbivores.

Figure 3.17. Herbivorous traces on P.

oceanica leaves (Buia et al. 2003)

33

3.3.1 Statistical analysis

With the aim of verifying the small-scale variability, and therefore between the transects of

each station, for the structural parameters, an ANOVA two-way nested was performed

following the sampling design, using R statistical software. This statistical analysis was

conducted after verifying the normality of data distribution with the Shapiro-Wilk test (p> 0.05)

and the Levene test was used to confirm homogeneity of variances (p> 0.05).

34

4. Results

4.1 Physical descriptors

4.1.1 Water conditions

The water temperatures recorded in the water column throughout the year showed the seasonal

pattern typical of temperate seas, with a minimum temperature of 14°C and a maximal one of

30.9°C (Fig. 4.1).

From October to February the temperatures recorded in the water column are homogeneous.

Bearing in mind that there is no fresh water supply and having verified that at different depths

even salinity remains homogeneous along the water column, it could be stated that during the

winter season the water masses had equivalent density. Considering the condition of high

hydrodynamism characteristic of that season, it could, therefore, be assumed that there was a

complete reshuffle affecting the entire water column.

Figure 4.1. Temperature time series along bathymetric gradient.

35

From February, with the advent of spring and hence rising air temperature, the structure of the

water masses changed. In fact, from this time of year, a stratification process of water masses

occurs, due to the superficial warming, which becomes increasingly evident in the summer

season, where it became clear the thermocline at a depth around -15m (Fig 4.3).

Figure 4.2. Salinity time series along bathymetric gradient.

0

5

10

15

20

25

30

10 15 20 25 30

Dep

th (

m)

Temperature (°C)

March

May

July

Figure 4.3. Temperature profiles,thermocline formation process.

36

The establishment of the thermocline, together with the abundant rains of the early months of

the year, induces a change in the density of water masses preventing its mixing; this is also

evident in the salinity chart (Fig. 4.2) two distinct water bodies can be identified above and

below -15m. There are hot waters with less salinity, less dense in the surface layer, and more

dense deeper, colder and saltier waters below. At the end of the summer season, it is perceived

by the data as the situation set up during the hottest period of the year, tends to return to the

winter homogeneity with the thermocline breaking due to the strong hydrodynamic regime and

the overall lowering of temperatures.

Another of the physical parameters under consideration was turbidity, in fact, under high

conditions, it is one of the drivers that guide the distribution and density of the P. oceanica

meadows. Values of this variable measured throughout the year were not high and were unlikely

to be able to affect the health of the plant. The only spikes that occur during the winter season

were related to isolated climatic events that have caused the particulate fraction present in the

sediment to be brought back into suspension (Fig. 4.4).

Figure 4.4. Turbidity time series along bathymetric gradient.

37

Concerning dissolved oxygen values, two types of patterns could be observed (Fig. 4.5). Except

for November, in accordance with the above, a uniformity of values for the entire water column

occurred. The situation beginned to diffract with the approach of spring and hence the growth

of phytoplankton on the shallower layers.

In fact, a large number of primary producers attracts its direct predators, zooplankton. These

microorganisms, located in the same bathymetric band of their prey, tend to consume large

amounts of oxygen, resulting in a decrease of it in surface concentrations (Gilly et al., 2013).

The great difference with the deep oxygen concentrations during the summer season was always

due to the presence of the thermocline that prevented the mixing of water, but was further

accentuated by P. oceanica's oxygen production peaks that are highest in the summer.

Figure 5.4 Turbidity time series along bathymetric gradient.

Figure 4.5 Dissolved oxygen time series.

38

4.1.2 Sediment analysis

From a preliminary visualization of the results gotten by the size particle analysis of the annual

series of the samples of sediment, it emerges that in all the three stations, the dominant

dimensional class is sand (Wentworth scale 2-0.063 mm).

The analysis of the annual series of sediment samples has initially been investigated through

the use of the ternary diagram of Shepard (1954), graphically represented using Grapher 9

software, that brings on the sides of a triangle the data ponder them some different

granulometric fractions and it has the purpose to classify the sediment in groups that have

different ecological meaning in relation to where they are placed. With this typology of analysis

the picked samples in the three stations lasting the whole arc of the year show to be very similar

among them and to belong all to the category of sands (Fig. 4.6, 4.7, 4.8).

Figure 4.6. Shepard triangle for C01 sampling station.

39

Figure 4.7. Shepard triangle for C02 sampling station.

Figure 4.8. Shepard triangle for C03 sampling station.

40

The following ternary diagram has been made, derived by the first one, which brings a different

classification, with the purpose to show the possible heterogeneities among samples, therefore

having a pure descriptive value. The weights of each dimensional class separated with the sieves

were declassified in different dimensional categories within the group of sands (Coarse sand

>1mm, medium sand 1-0.250mm, fine sand < 0.250mm), considering that they constitute

around the 90% of the total weight in all samples. Also in this case samples are results to be

very homogeneous inside the same stations during the whole year (Fig. 4.9, 4.10, 4.11).

Figure 4.9. Sands classification triangle for C01 sampling station.

41

Figure 4.10. Sands classification triangle for C02 sampling station.

Figure 4.11. Sands classification trangle for C03 sampling station.

42

The variability during the year, inside the stations at different depth, has been investigated using

the weights related to every level of the battery of sieves in relationship to the time. With such

subdivision, following the calculation of the Pearson’s correlation index, meaningful tendencies

to temporal variation does not appear, for the C01 and C03 station, while instead meaningful

results are gotten by the analysis of the C02 station. At C02 a positive correlation between time

and sediment fraction of 0.5mm, and a negative correlation between time and sediment >0.5mm

was found. During the year, from the winter toward the summer, there is, therefore, a situation

of increase of thin sand and a diminution of coarse sand.

Everything seems to point out that in the C01 and C03 stations, in the whole arc of the year,

there is a rather stable sediment structure suggesting that hydrodynamism is not particularly

subject to seasonal variations, while the C02 station, show a correlation between time and

different dimensional classes and therefore a temporal pattern.

The initial hypothesis of seasonal variation in the sediment particle size, seems denial for the

superficial and deep station, but not for the intermediary one, but to affirm it with certainty

further studies replicated in time are needed.

Proceeding with the results of the granulometric parameters, giving them information on the

hydrodynamic conditions, they confirm a condition of elevated/medium hydrodynamism in the

first and third station and a scarce/weak hydrodynamism in the intermedite one during the whole

year. Besides, it appears clear that in the three stations the absence of a selective agent,

contributes to a bad classation of the sediments (Tab. 4.1).

The peculiar hydrodynamic situation in the zone C02 should subsequently be investigated. It

could be that P. oceanica meadow, reducing the energy of the waves, already less intense in the

summer period, facilitates an appropriation of the thin particles in this zone.

43

Station

Sample

Mdø

σSk

KFh

C01

10.

110.

76m

ildly

cla

ssed

-0.2

3as

ymm

etri

cal v

ery

nega

tive

high

ene

rgy

0.88

plat

icur

tic

0.31

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

20.

571.

14m

ildly

cla

ssed

0.09

asym

met

rica

l ver

y po

siti

velo

w e

nerg

y2.

04m

esoc

urti

cse

dim

ent s

ubje

cted

to

high

ene

rgy

1.61

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

30.

151.

15m

ildly

cla

ssed

-0.0

9sy

mm

etri

cal

high

ene

rgy

1.60

mes

ocur

tic

sedi

men

t sub

ject

ed t

o hi

gh e

nerg

y0.

98m

ediu

m o

r str

ong

hyd

rody

nam

ism

C01

4-0

.12

1.77

bed

clas

sed

0.32

asym

met

rica

l ver

y po

siti

velo

w e

nerg

y1.

28pl

atic

urti

c0.

40m

ediu

m o

r str

ong

hyd

rody

nam

ism

C01

5-0

.01

1.23

mild

ly c

lass

ed-0

.06

sym

met

rica

lhi

gh e

nerg

y1.

54m

esoc

urti

cse

dim

ent s

ubje

cted

to

high

ene

rgy

0.86

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

60.

191.

21m

ildly

cla

ssed

0.01

sym

met

rica

llo

w e

nerg

y1.

59m

esoc

urti

cse

dim

ent s

ubje

cted

to

high

ene

rgy

0.96

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

70.

061.

15m

ildly

cla

ssed

0.00

sym

met

rica

llo

w e

nerg

y1.

58m

esoc

urti

cse

dim

ent s

ubje

cted

to

high

ene

rgy

0.95

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

8-0

.12

0.95

mild

ly c

lass

ed0.

14as

ymm

etri

cal p

osit

ive

low

ene

rgy

1.22

lept

ocur

tic

0.63

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

9-0

.10

1.16

mild

ly c

lass

ed-0

.04

sym

met

rica

lhi

gh e

nerg

y1.

49m

esoc

urti

cse

dim

ent s

ubje

cted

to

high

ene

rgy

0.84

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

100.

301.

03be

d cl

asse

d0.

01sy

mm

etri

cal

low

ene

rgy

1.59

very

lept

ocur

tic

high

hyd

rody

nam

ism

1.05

med

ium

or s

tron

g h

ydro

dyna

mis

m

C01

110.

061.

21m

ildly

cla

ssed

-0.0

8sy

mm

etri

cal

high

ene

rgy

1.54

mes

ocur

tic

sedi

men

t sub

ject

ed t

o hi

gh e

nerg

y0.

87m

ediu

m o

r str

ong

hyd

rody

nam

ism

C01

120.

341.

17m

ildly

cla

ssed

-0.0

5sy

mm

etri

cal

high

ene

rgy

1.68

mes

ocur

tic

sedi

men

t sub

ject

ed t

o hi

gh e

nerg

y1.

12m

ediu

m o

r str

ong

hyd

rody

nam

ism

C02

1-0

.08

1.71

bed

clas

sed

0.47

asym

met

rica

l ver

y po

siti

velo

w e

nerg

y1.

33le

ptoc

urti

c0.

50m

ediu

m o

r str

ong

hyd

rody

nam

ism

C02

20.

311.

90be

d cl

asse

d0.

38as

ymm

etri

cal v

ery

posi

tive

low

ene

rgy

0.67

plat

icur

tic

-1.0

3hy

drod

ynam

ism

alm

ost n

il

C02

3-0

.52

1.41

bed

clas

sed

0.35

asym

met

rica

l ver

y po

siti

velo

w e

nerg

y1.

47le

ptoc

urti

c0.

73m

ediu

m o

r str

ong

hyd

rody

nam

ism

C02

40.

051.

03be

d cl

asse

d0.

19as

ymm

etri

cal p

osit

ive

low

ene

rgy

1.47

lept

ocur

tic

0.89

med

ium

or s

tron

g h

ydro

dyna

mis

m

C02

5-0

.10

1.93

bed

clas

sed

0.49

asym

met

rica

l ver

y po

siti

velo

w e

nerg

y0.

70pl

atic

urti

c-0

.92

med

ium

or s

tron

g h

ydro

dyna

mis

m

C02

60.

931.

89be

d cl

asse

d0.

20as

ymm

etri

cal p

osit

ive

low

ene

rgy

0.62

very

pla

ticu

rtic

low

hyd

rodi

nam

ism

, sed

imen

tati

on-1

.16

hydr

odyn

amis

m a

lmos

t nil

C02

70.

241.

81be

d cl

asse

d0.

44as

ymm

etri

cal v

ery

posi

tive

low

ene

rgy

0.72

plat

icur

tic

-0.7

7hy

drod

ynam

ism

alm

ost n

il

C02

82.

641.

98be

d cl

asse

d-0

.51

asym

met

rica

l ver

y ne

gati

vehi

gh e

nerg

y0.

63ve

ry p

lati

curt

iclo

w h

ydro

dina

mis

m, s

edim

enta

tion

-1.2

2hy

drod

ynam

ism

alm

ost n

il

C02

91.

401.

96be

d cl

asse

d-0

.05

sym

met

rica

lhi

gh e

nerg

y0.

62ve

ry p

lati

curt

iclo

w h

ydro

dina

mis

m, s

edim

enta

tion

-1.2

3hy

drod

ynam

ism

alm

ost n

il

C02

100.

651.

94be

d cl

asse

d0.

24as

ymm

etri

cal p

osit

ive

low

ene

rgy

0.62

very

pla

ticu

rtic

low

hyd

rodi

nam

ism

, sed

imen

tati

on-1

.21

hydr

odyn

amis

m a

lmos

t nil

C02

110.

132.

01ve

ry b

ed c

lass

ed0.

36as

ymm

etri

cal v

ery

posi

tive

low

ene

rgy

0.64

very

pla

ticu

rtic

low

hyd

rodi

nam

ism

, sed

imen

tati

on-1

.18

hydr

odyn

amis

m a

lmos

t nil

C02

120.

611.

85be

d cl

asse

d0.

29as

ymm

etri

cal p

osit

ive

low

ene

rgy

0.64

very

pla

ticu

rtic

low

hyd

rodi

nam

ism

, sed

imen

tati

on-1

.07

hydr

odyn

amis

m a

lmos

t nil

C03

10.

480.

73m

ildly

cla

ssed

-0.0

2sy

mm

etri

cal

high

ene

rgy

1.49

lept

ocur

tic

1.10

med

ium

or s

tron

g h

ydro

dyna

mis

m

C03

20.

501.

09be

d cl

asse

d-0

.03

sym

met

rica

lhi

gh e

nerg

y1.

65ve

ry le

ptoc

urti

chi

gh h

ydro

dyna

mis

m1.

16m

ediu

m o

r str

ong

hyd

rody

nam

ism

C03

30.

490.

90m

ildly

cla

ssed

0.02

sym

met

rica

llo

w e

nerg

y1.

54ve

ry le

ptoc

urti

chi

gh h

ydro

dyna

mis

m1.

11m

ediu

m o

r str

ong

hyd

rody

nam

ism

C03

40.

361.

04be

d cl

asse

d-0

.10

sym

met

rica

lhi

gh e

nerg

y1.

21le

ptoc

urti

c0.

56m

ediu

m o

r str

ong

hyd

rody

nam

ism

C03

50.

611.

13be

d cl

asse

d0.

08sy

mm

etri

cal

low

ene

rgy

1.89

very

lept

ocur

tic

high

hyd

rody

nam

ism

1.42

med

ium

or s

tron

g h

ydro

dyna

mis

m

C03

60.

371.

03be

d cl

asse

d-0

.12

asym

met

rica

l neg

ativ

ehi

gh e

nerg

y1.

29le

ptoc

urti

c0.

67m

ediu

m o

r str

ong

hyd

rody

nam

ism

C03

70.

520.

95m

ildly

cla

ssed

-0.3

5as

ymm

etri

cal v

ery

nega

tive

high

ene

rgy

1.13

lept

ocur

tic

0.52

med

ium

or s

tron

g h

ydro

dyna

mis

m

C03

80.

490.

86m

ildly

cla

ssed

-0.3

9as

ymm

etri

cal v

ery

nega

tive

high

ene

rgy

1.09

mes

ocur

tic

sedi

men

t sub

ject

ed t

o hi

gh e

nerg

y0.

53m

ediu

m o

r str

ong

hyd

rody

nam

ism

C03

90.

620.

88m

ildly

cla

ssed

-0.2

0as

ymm

etri

cal n

egat

ive

high

ene

rgy

1.42

lept

ocur

tic

0.98

med

ium

or s

tron

g h

ydro

dyna

mis

m

C03

100.

571.

08be

d cl

asse

d0.

24as

ymm

etri

cal p

osit

ive

1.75

very

lept

ocur

tic

high

hyd

rody

nam

ism

1.25

med

ium

or s

tron

g h

ydro

dyna

mis

m

C03

110.

390.

84m

ildly

cla

ssed

-0.1

4as

ymm

etri

cal n

egat

ive

high

ene

rgy

1.26

lept

ocur

tic

0.78

med

ium

or s

tron

g h

ydro

dyna

mis

m

C03

120.

521.

02be

d cl

asse

d-0

.15

asym

met

rica

l neg

ativ

ehi

gh e

nerg

y1.

46le

ptoc

urti

c0.

96m

ediu

m o

r str

ong

hyd

rody

nam

ism

Table 4.1. Falk&Ward parameters results.

44

4.3 P. oceanica monitoring results

The results obtained for each descriptor of the P. oceanica meadows are presented as explained

in the section Materials and methods.

Passing through the results of the physiographical descriptors, from a bathymetric point of

view, the meadow of Cala Racò is located within the depth range of 5-22 m, and was

characterized by a predominantly sandy bottom, with large rocky blocks. In this location, the

meadow showed some signs of discontinuities and clearings of various form and size, within

one of which there was a wreck of a small fishing boat. Since it is characterized by the presence

of a continuous and homogeneous matte, the bed can be classified ad “flat and continuous”

(“herbier de plain”) (Pergent and

Pergent-Martini, 1995). The lower

limit was fairly sinuous and develops

mainly along the isobath of -22

meters and was classified as a "net

limit" as it was characterized by a

sharp meadow break, the presence of

orthotropic and plagiotropic

rhizomes and the lack of "matte"

(Fig. 4.12).

Instead, with regard to the north side of the Peñón de Ifach, the patch of P. oceanica in which

station B was placed was entirely developed at -24m, on a sandy bottom where there were huge

stone blocks on which P. oceanica tufts were present. Here it is possible to identify an hilly bed

(“herbier de colline”), characterized by patches (“small islands”) of matte, covered with green

vegetation which rise up from the surrounding sandy areas that are devoid of vegetation

(Boudouresque et al., 1985). Here the lower limit (Fig. 4.13) was classified as a "regressive

limit" characterized by the presence of dead matte, on which isolated live shoots persist. A limit

of this type indicates a regression of the meadow which is often related to increased turbidity.

Figure 4.12. Limit of the meadow of Cala Racò (A3 station).

45

The reef-meadow extended along the entire coastline in the bathymetric band ranging from -

5m to -9m; in this case station C was placed at the lower limit of the meadow and it was

classified as "erosion limit" (Fig. 4.14) as it was characterized by the presence of a clear "matte"

step (Fig 4.15), with prevalence of orthotropic rhizomes.

Figure 4.13. Limit of the patch of P. oceanica on the north side, B station.

Figure 4.14. Limit of the reef-meadow, C station. Figure 4.15. Detail of the step of "matte" in C station'2 limit.

46

Between the structural descriptors, the shoot density values of the stations were

heterogeneous, they ranged from a minimum mean value of 261.33 ± 14.11 shoot m-2, in the

second transect of B station, and maximum mean value of 1237.33 ± 244.93 shoot m-2 in the

fourth transect of C station, as shown in Figure 4.16.

The average of Covering for each station during the study period is graphically represented in

figure 4.17, with its relative standard error. The covering values in these stations ranged

between a minimum mean value of 6.94 ± 1.93 % in the last transect of the deepest station (B)

on the north side of the Peñón de Ifach and maximum mean value of 66.69 ± 4.83 % in the

second transect of the shallower station in Cala Racò (A1).

0

200

400

600

800

1000

1200

1400

A1 A2 A3 A4 B C

Shoot density (Shoot m-2)

1 2 3 4 5 6

Figure 4.16. Mean Shoot deansity values for each transect of each station.

0

10

20

30

40

50

60

70

80

A1 A2 A3 A4 B C

Covering (%)

1 2 3 4 5 6

Figure 4.18. Mean Covering values for each transect of each station.

47

The values of Global Density, calculated from the density and covering values, as presented in

the previous section 3.3, ranged between minimum mean value of 26.27 ± 6.09 shoot m-2, in

B station and maximum mean value of 700.67 ± 103.85 shoot m-2 at C station, following the

pattern of the maximum density previously exposed (Fig 4.18).

Subsequently to the calculation of the average global density for each station, it was possible

to compare the data with those reported in the literature by Pergent et al., (1995). In fact, these

authors formulated a broad classification of the health status of P. oceanica meadows. Density

is related to many environmental parameters: depth, turbidity, anthropogenic disturbance, etc.

In this classification "balanced meadows", where the density is standard or exceptional, are

distinguished from "disturbed meadows" or "heavily disturbed meadows", where density,

limited by several factors, is low (Fig 4.19).

0

100

200

300

400

500

600

700

800

900

A1 A2 A3 A4 B C

Global density (Shoots m-2)

1 2 3 4 5 6

Figure 4.18. Mean Global density values for each transect of each station.

48

It turns out that half of the density values measured at the stations were in the standard, while

the others showed very low or unusual values. Reporting the density values thus analyzed, to

the meadow to which they belong, it could be said that the Cala Racò (A1, A2, A3, A4) meadow

was ranked as "balanced" at intermediate bathymetry and "disturbed" both in surface and in the

lower limit; while the meadow on the north side of the Peñón de Ifach, the one in which B

station was placed was at the boundary between "disturbed" and "heavily disturbed" while the

one in which C station was localized was "balanced".

The last structural descriptor analyzed was the burial of the shoots. These measures, done in all

the transect of each station, are shown in Figure 4.20 with its standard error. In all stations, a

Figure 4.19. P. oceanica status, modified from Pergent et al. 1995.

0

2

4

6

8

10

12

A1 A2 A3 A4 B C

Burial (cm)

1 2 3 4 5 6

Figure 4.20. Mean Burial values for each transect of each station.

49

positive trend of the parameter was evident, which coincides with a slight disintegration of the

shoots.

For all structural descriptors, due to the nature of the sampling design, a two-way nested

ANOVA was performed, which revealed significant differences only between stations, but not

among the transects conducted within them (Tab. 4.2); therefore it was possible to exclude a

significant variation among transects within stations.

Below are the results relating to the functional descriptors, thus all those obtained from the

phenological analysis of leaves and shoots, taken at each station.

The average number of leaves per shoot was measured at all stations and it is shown in Figure

4.21 with its relative standard error. As is possible to see, the number of leaves ranges between

a minimum of 4.6 ± 0.13 recorded at station A1, to a maximum value of 6.67 ± 0.34 at B station.

Data were compared to what was reported in the literature, through a t-test, but no homogeneity

was found. In fact, the average number of leaves per shoot reported from Buia et al., (2003) is

of 8 leaves in shallow zones (less than -15 m) and 7 leaves in deep zones (more than -15 m).

Our data do not comply with the pattern described in the literature, which foresees a decrease

in the number of leaves per shoot along the bathymetric gradient, but it seems to be opposed as

shown in Figure 4.22.

ANOVA Density Alpha 0.05

SS df MS F p-value sig

Transects 133668.9 5 26733.77 0.21732 0.952354 no

Stations 3690468 30 123015.6 21.38628 3.05E-25 yes

Within 414149.8 72 5752.081

Total 4238287 107 39610.15

ANOVA Covering Alpha 0.05

SS df MS F p-value sig

Transects 4941.152 5 988.2304 0.235562 0.943742 no

Stations 125856 30 4195.201 9.784884 2.55E-30 yes

Within 138912.7 324 428.743

Total 269709.9 359 751.281

ANOVA Burial Alpha 0.05

SS df MS F p-value sig

Transects 132.2681 5 26.45361 0.870643 0.512325 no

Stations 911.5194 30 30.38398 3.49386 7.34E-09 yes

Within 3443.772 396 8.696393

Total 4487.559 431 10.41197

Table 4.2. ANOVA results for (1) Shoot density, (2) Covering and (3) Burial.

50

The average values of P. oceanica leaf length in the investigated meadows ranged between a

minimum mean value of 34.08 ± 2.47 cm in the deepest station (B); to the maximum mean

value of 68.32 ± 2.34 cm in the shallower station (A1). All values are listed in Figure 4.23 with

their standard errors. In this case, the pattern found complies with what is reported in the

literature. In fact, the leaf length decreased along the bathymetric gradient as shown in Figure

4.24. Moreover, Pearson's correlation index showed a very high degree of correlation between

the measured variable and the environmental variable (r = -0.83, ρ < 0.05).

A1

C

A2

A4 A3

B

0

1

2

3

4

5

6

7

5 10 15 20 25

Depth (m)

N° leaves shoot-1

A1

C

A2

A4A3

B

0

10

20

30

40

50

60

70

80

5 10 15 20 25

Depth (m)

Leaf lenght (cm)

0

10

20

30

40

50

60

70

80

A1 A2 A3 A4 B C

Leaf length (cm)

0

1

2

3

4

5

6

7

8

A1 A2 A3 A4 B C

N° Leaves shoot-1

Figure 4.21. Mean values of number of leaves Figure 4.22. Number of leaves per shoot, along bathymetic gradient.

per shoot.

Figure 4.24. Mean Leaf length values in each Figure 4.25. Leaf length along bathymetric gradient.

station.

51

About leaves width values, they ranged between 0.8 and 1.1 cm, with an average value of 0.95

cm in all stations; a t-test showed homogeneity with what is reported in the literature.

For what concerns the derived descriptors, calculated values for the mean leaf surface parameter

for shoot are shown in Figure 4.26 with the corresponding standard errors; these ranged from a

minimum of 226.74 ± 10.77 cm2 shoot-1 (B) up to a maximum of 319.70 ± 14.68 cm2 shoot-1

(A2). Also in this case, the trend of the variable along the bathymetric gradient has been studied

to verify consistency with the pattern described in the literature, which shows a decrease as the

depth increases. This was verified, as can be seen in Figure 4.26, and subsequently the

calculation of the Pearson correlation index, showed that the two variables were closely related

(r = -0.84, ρ < 0.05).

Concerning the measures regarding the status of leaf apex, it showed great heterogeneity

between the stations (fig), with maximum values of leaves whose apex seemed to be broken

because of the action of some herbivore reaching 70.25 ± 4.07% in the superficial station A1,

as shown in Figure 4.27. Later, the values of the herbivorous rate were compared to the

bathymetric gradient. Even in this case, it was possible to detect a negative relationship between

the two variables; in fact, as can be seen in Figure 4.28, as the depth increased, decreased the

number of leaves showing traces due to the herbivorous activity. Between the two variables, a

no correlation was found, always tested by the Pearson correlation index.

A1A2

A3A4

B

C

0

50

100

150

200

250

300

350

400

5 10 15 20 25

Depth (m)

Leaf area/shoot (cm2 shoot-1)

0

50

100

150

200

250

300

350

400

A1 A2 A3 A4 B C

Leaf area/shoot

(cm2 shoot-1)

Figure 4.25. Mean Leaf area/shoot values in

each station. Figure 4.26. Leaf area/shoot values along bathymetric gradient

52

Lastly, the values of the two derived descriptors, LAI and Coefficient "A", calculated in each

station are given in Table 4.3. For all stations, the LAI values were consistent with those

reported in the literature (1.1 <LAI <29 (Buia et al., 2003)), except for station B showing a

rather low value.

Stations A1 A2 A3 A4 B C

Leaf Area

Index (m2 m-2) 9.890576 12.1686 2.470087 7.933146 0.864226 16.46578

Coefficient “A” 0.769231 0.574324 0.616216 0.857143 0.267606 0.695402

Table 4.3. LAI and Coefficient "A" values in each station.

0

10

20

30

40

50

60

70

80

90

100

A1 A2 A3 A4 B C

Apex status (% leaves shoot)

% Salpas % Paracentrotus % Whole % Broken

Figure 4.27. Apex status in each station.

A1

A2A3

A4

B

C

0

10

20

30

40

50

60

70

80

90

5 10 15 20 25

Depth (m)

Herbivous rate (% leaves shoot-1 )

Figure 4.29. Herbivous rate along bathymetric gradient.

53

5. Discussion

By analyzing the physical descriptors, the physiochemical parameters of the water, such as

temperature, salinity and turbidity, and comparing them with what is reported in the literature,

it can be stated that the waters surrounding the Peñón de Ifach Natural Reserve fit with the

expectation for a non overdeveloped Mediterranean coastal area. The salinity values recorded

are consistent with the optimal conditions for plant life, the latter being able to tolerate a wide

variation range, provided that it is above 33 ‰. As for turbidity, which apart from individual

seasonal events does not exceed 0.5 FTU, it can be concluded that its value does not deteriorate

the state of the meadow. As far as temperature is concerned, variations were recorded between

a minimum of 14 °C in January up to a maximum of 30.9 °C in August. These values fall within

the temperature range tolerated by P. oceanica which, according to observations conducted by

Augier et al., (1980), is able to withstand conditions between 9 °C and 29.2 °C. However, it can

be noted that the maximum surface temperature recorded in the summer months is close to the

maximum tolerable from the plant. Mayot et al. (2005) suggest that the increase in seawater

temperature that is currently observed throughout the world (Salat et Pascual 2002) could have

a harmful effect on P. oceanica. Temperature affects almost every aspect of seagrass

metabolism, growth and reproduction, and also has important implications for geographic

patterns of seagrass species abundance and distribution. The rise in temperature in the next 25

years will result in a projected increase in sea level between 10 and 15 cm, mostly because of

thermal expansion of the ocean waters and, to a lesser extent, because of melting glaciers and

ice sheets. The rise in sea level may have numerous implications for circulation, tidal amplitude,

current and salinity regimes, coastal erosion and water turbidity, each of which could have

major negative impacts on local seagrass performance (Borum 2004). Long-term forecasts

regarding the change in salinity in relation to global temperature rise suggest that in the

Mediterranean, where evaporation processes are predominant to precipitation, an increase of

about 0.5 PSU in ten years may be expected. These predictions, unlike those for temperature,

are not ecologically worrisome for P. oceanica meadows; in fact, it has been shown that they

can survive even in hypersalinity conditions such as Tunisian lagoons where salinity is around

44 ‰ (Boudouresque et al., 2012).

About the hydrodynamic conditions, investigated by sediment sample analysis, they show no

particular criticality for the survival of P. oceanica meadows in this area. Although a seasonal

pattern in sediment dynamics is evident, neither the winter nor the summer season are

characterized by a hydrodynamism that significantly impacts on the nature of the substrate and

54

then on the growth of the plant. As evident in the results of C02 monitoring station, the meadow

is able to mitigate the energy of the wave motion in the summer season fulfilling its role in

effectively absorb hydrodynamism. Field experiments have shown that a meadow is able to

reduce by the 20 % the velocity of currents above it (Gacia and Duarte 2001).

Despite the results of the physical descriptors regarding the environmental condition highlight

an acceptable situation for the growth of P. oceanica, on the basis of the observations made in

this study on the physiographical, structural and functional descriptors of the seagrass it is noted

that ecological status varies among the examined meadows.

With regard to the physiographical descriptors, on the south side of Peñón de Ifach, where

stations A are located, the upper limit is the direct consequence of the geomorphology and the

rocky nature of the seabed in its closest part to the coast. On the north side, however, where the

station B is located, the presence of clearances and low densities could be related to the shape

of the emerged coast of the natural park, which is characterized by vertical walls shading the

backdrops, probably preventing the expansion of the meadow towards the coast. As for the reef-

meadow in which station C is located, the upper limit is the consequence of the probability of

the meadow being exposed to drying. The “net”, “regressive” and “erosive” lower limits for the

A, B, C monitored meadows are relatively shallow, despite the remarkable transparency of the

water, but no historical observations on the meadows exist and we con not made any

consideration on the current dynamics of these limits.

In relation to the structural parameters, Global density recorded varies among stations,

however, the southern and reef meadow can be classified as "dense", while the one named B as

a “semi-meadow”. By comparing the densities observed at each station with the corresponding

depths (Pergent et al., 1995) (Fig. 4.19), the stations C, A2 and A3 are defined as “in

equilibrium” state, while A1, A3 and B are on the limits between a “disturbed” and “very

disturbed” condition. Within the same meadow (Cala Racò A) different status were observed

in separate patches. This highlights the possibility of disturbances acting on the meadow health

at very small scale (e.g. anchoring activity), as already supposed by Guillén et al., (2013).

“Disturbed” conditions of B station were observed in a shaded area where it is probably due to

the low solar radiance. In relation to the values obtained regarding P. oceanica shoots burial in

all the stations, it can be stated that, although they are always positive, they are not such to

permit the predominance of erosive processes in place, but rather indicate a dynamic balance

between sedimentation processes and growth of the plant.

55

According to Buia et al., (2003) on the values of functional descriptors (leaves/shoots, leaves

length and leaf area/shoot) including derived descriptors(leaf surface index (LAI)), taking into

account the normality ranges reported from the point of view of leaf growth, stations can be

considered in optimum conditions, with the only exception of station B. This station, in fact,

reports a value of LAI rather low compare to what is reported in the literature. This may still be

the result of lower solar radiation in the area where the meadow is located that may affect the

photosynthetic activity of the plant. The coefficient "A", which mainly expresses the combined

effect of the mechanical action of hydrodynamism on leaves and grazing of herbivores, is

consistent with expected values related to the depth of the stations. In fact, the percentage of

broken apices or bites is higher in the more superficial stations and decreases along the

bathymetric gradient. Overall the status of P. oceanica meadows in Calpe bay is not worrying.

The results obtained and the evaluations made in this study provide a valuable baseline for

future studies and comparisons, in the framework of the monitoring studies needed to keep track

of the dynamics of the Calpe bay meadows. The results revealed that the ecological status of

the Cala Racò meadow is not particularly good, but this is not surprising. Guillén et al., (2013)

in relation to a ten-year monitoring network, reported that P. oceanica meadows located in

Calpe are in less than optimal conditions. Despite this, there is a clear trend of an improvement,

identified by these authors using the Global density and Covering parameters until 2011,

although it is very slow (Fig 5.1).

The present study seems to confirm the positive trend highlighted by Guillén et al., (2013),

showing even higher values for the two parameters considered. It can, therefore, be stated that

P. oceanica meadow in Calpe bay, from more than 15 years, are facing a recovery process

following a disturbance event in the past. These events could consist of the construction of the

“El Racò” fishing port, dating back to the first half of the 20th century, or the dumping of waste

in the sea-front just outside the harbor, occurring up about 20 years ago. Due to the low

resilience of P. oceanica (Procaccini et al., 1996), the species keeps a strong and very long

Figure 5.1. Trends of Global density and Covering in the period 2002-2011 in Cala Racò meadow. (Modified from Guillén et

al. 2013)

56

biological memory of past events of regression: the recovery of a regressed P. oceanica

meadow may take several years (Boudouresque et al., 2006), independently from the quality of

the water.

Data collected in this study were compared with those collected by Guillén et al., (2013), while

this is not always possible due to the heterogeneity of the methodologies often used. Since

different efforts have been made to carry out monitoring studies in several countries in order to

protect legally P. oceanica, it would be desirable to have a major homogeneity in the protocols

to be used, at least at European level. Proper management of the P. oceanica meadows, in fact,

would require standardized methodologies of study, to be applied by both researchers and

administrators, enabling comparable results on the scale of the whole Mediterranean basin.

Considering the enormous variety of the methodologies, Pergent-Martini et al., (2005) (Fig 5.2)

Figure 5.2. Recapitulative plan of the main descriptors of Posidonia oceanica, with the measured parameters the methods of

investigation: (1) Meinesz et al. (1988); (2) Lefevre et al. (1984); (3) Pasqualini et al. (1997); (4) Mc Kenzie et al. (2003); (5)

Augier et al. (1984); (6) Boudouresque et al. (2000); (7) Balduzzi et al. (1981); (8) Dauby and Poulicek (1995); (9) Cinelli et

al. (1984); (10) Morri (1991); (11) Buia et al. (2003); (12) Giraud (1977); (13) Giraud (1979); (14) Drew and Jupp (1976);

(15) Blanc (1956); (16) Clairefond and Jeudy De Grissac (1979); (17) Willsie (1987); (18) Pergent et al. (1995); (19) Pergent

(1990); (20) Duarte (1991b); (21) Cebrian et al. (1994); (22) Mateo et al. (1997); (23) Pergent et al. (1989); (24) Panayotidis

et al. (1981); (25) Romero (1986); (26) Meinesz and Laurent (1978); (27) Duarte and Kirkman (2003); (28) Francour et al.

(1999); (29) Ramos-Martos and Ramos-Espla (1989); (30) Pasqualini et al. (2000); (31) Blanc-Vernet (1984); (32) Russo and

Vinci (1991); (33) Harmelin-Vivien and Francour (1992); (34) Hamoutene et al. (1995); (35) Ferrat et al. (2002); (36) Mateo

and Sabate (1993); (37) Gobert et al. (1995) and (38) Romeo et al. (1995). From Pergent-Martini et al. (2005).

57

made a review on the main descriptors of P. oceanica, with the measured parameters and the

methods of investigation, used in 41 laboratories situated all over the Mediterranean coasts.

They showed that some descriptors, as density and bathymetric positions of the meadow,

benefit from a protocol that is applied, quite homogeneously, by all the laboratories, but this is

not the case for all descriptors. However, concerning the measurement of meadows density, the

type of quadrat and/or the number of replications varied from one laboratory to another.

Anyway, the acquisition of a descriptor is only the first step in its use: an interpretation scale is

required to make the descriptor effective.

With respect to density, for example, in the literature there is a large number of indicators used

to classify the status of the meadows. The scale of Giraud (1977) remains in common use

because it is simple to implement (six classes with precisely defined markers) (Pergent-Martini

et al., 2005). Nevertheless, it should be noticed that this scale does not take into consideration

the normal decrease in meadow density in function of depth or the type of substrate, which are

the most important parameters driving the distribution of this plant. The attempt of classifying

proposed by Romero-Martinengo (1985), which introduced the effect of depth, was difficult to

apply because of the lack of some of the parameters needed to calculate it (e.g. coefficient of

light attenuation). The scale proposed by Pergent et al., (1995) and used in this work, includes

the depth parameter, by means of a logarithmic factor, on the basis of bibliographical data

concerning stations submitted to different levels of human pressure. Its aim is both to compare

stations situated at different depths (this cannot be done with the scale of Giraud, 1977) and to

evaluate the ‘‘normal’’ level of density and the quality of the environment. However, it needs

to be improved by incorporating a greater quantity of features and also by a more precise

determination of the human characteristics of the site and the type of bottom (e.g. soft or hard)

(Pergent-Martini et al., 2005). The sampling design may be also a critical issue for the validity

of the results obtained. Because some descriptors (such as meadow cover or shoot density) may

demonstrate a high variability at small or medium spatial scales (Panayotidis et al., 1981;

Balestri et al., 2003), Fernández-Torquemada et al., (2008) recommend utilizing a nested

sampling design with an adequate spatial replication. Furthermore, seasonal variation at the

community, population, and individual plant level must be taken into account. Descriptors such

as shoot foliar surface and epiphyte biomass should be sampled during a fixed period of the

year to avoid any confounding effect of seasonality.

58

For a selection of metrics to be applied in future monitoring programmes, especially for those

on large spatial scale, also cost-effectiveness is an important issue, and therefore the metrics

should be easily measured and applied. Obviously, the most convenient techniques vary in

relation to the research goals. When the scope is to provide detailed data on distribution and

change in seagrass areas or to estimate the biomass, the best choice is high-resolution mapping.

Aerial photography is the most common remote sensing method for seagrass mapping studies

and for monitoring over time, while satellite data are valued for large-scale localization

investigations. Airborne scanners may also provide a high accuracy and this technique is

becoming gradually more competitive (Krause-Jensen et al., 2004). However, when the aims

of the monitoring programme are to obtain higher resolution data or samples collection, it is

necessary to have a SCUBA diving team. To lower the management costs of such a team, for

example, some Spanish communities (e. g. Región de Murcia) have used volunteer groups to

carry out annual monitoring of meadows. The participation of voluntary divers in biological

monitoring programs must guarantee an acceptable data quality and reliability so that they can

be used for monitoring purposes and in the political decision processes that affect the

management of human activity on the coast. But, to achieve this, these projects must gather a

series of basic conditions: (a) provide an adequate theoretical and practical training of the

volunteers, (b) encourage the interest and motivation of the volunteer to be rigorous with the

tasks performed, (e) use simple and robust measurements, (d) apply control measures to

quantify the error of the measurements made by the voluntary, (e) be coordinated by groups or

entities with recognized scientific training.

Involvement of volunteers provides a future potential for a participatory monitoring network,

supporting the implementation of scientific knowledge on marine ecosystems. Moreover, it also

contributes to their future conservation, since this may be achieved only with the support of the

citizens and of the society. The Monitoring Networks have, therefore, the commitment to

become vehicles for transmitting scientific knowledge and awareness on current problems that

threaten our marine ecosystems. In addition, through their active participation, sports diver are

getting involved directly in tasks of conservation of habitats and species that have aroused their

admiration. Finally, in the medium and long term, the role that this type of activities can have

is the diversification of underwater tourism. Recreational diving has undergone overcrowding

and its concentration in marine "sanctuaries" may cause the deterioration of the natural values

of the marine protected areas, as has already been demonstrated in many places (Ruiz et al.,

59

2012). In this sense, the education of the sports diver, in particular, and the citizen, in general,

in environmental issues is a fundamental aspect.

60

6. Conclusion

With the aim of identifying and then sustaining the health status of the meadows of Calpe Bay,

it was considered appropriate to set up a monitoring network as presented in this paper.

The underwater meadows of Posidonia oceanica are especially vulnerable to the impact of

human activities, a property that, together with its wide geographical distribution, has made

them excellent candidates as a biological indicator of the state of conservation of coastal marine

ecosystems. It is also one of the most important ecological habitats in the Mediterranean and,

paradoxically, of the most threatened due to the development of human activity on the coast.

Consequently, they benefit from a protection status in most of the Autonomous Communities

that make up the Spanish Mediterranean coast and are considered priority protection habitats in

the Community Directive and in the Barcelona Convention.

For this reason, it is important to create monitoring networks that have adequate characteristics.

A Monitoring Network for the P. oceanica meadows should consist of a series of fixed points

(sampling stations), distributed along the coast, which are visited periodically to make a series

of measurements in order to know the health status of the habitat or populations targeted study

and its long-term evolution. For a project of these characteristics to be viable, a series of basic

requirements must be met:

1. Cover broad temporary scales (minimum 10 years).

2. Contemplate a wide network of points representative of the environmental conditions in

which the habitat is located and that allow us to infer changes originated by human activity

from those that are caused by natural factors.

3. Use easy-to-obtain measurements with effective, robust and standardized methods that allow

the comparison of results obtained by different samplers, in different geographical areas and in

different years, with little error.

61

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